The present invention relates to a fuel supply system for a gas turbine engine, more particularly such a system having a valve controlled discharge conduit to prevent heated fuel in the fuel injector conduits from being injected into the combustion chamber wherein the engine is stopped.
Aircraft, including the turbojet engines which act as power plants, are subjected to exceedingly strict safety regulations. Such safety regulations mandate that malfunctions of the fuel supply systems are designed to preclude multiple or latent malfunctions. However, operational requirements may require a design that does not fully meet the malfunction analysis. Obviously, such design choices incur only at a secondary level and do not impair the safety of the aircraft.
In the case of a design for a fuel injector manifold and associated fuel injectors, operational requirements dictate that the fuel supply system and fuel injector conduits not be purged when the jet engine is stopped in order to minimize subsequent engine start-up time. If the fuel were purged from the manifolds and injectors, it would be necessary to have these components again be filled with fuel prior to starting the engine. Such additional fuel filling time, when added on to the ordinary engine start-up time, results in an excessive delay.
However, when a jet engine is stopped and the high pressure portion of the fuel system is not purged, heat radiating from the stopped engine will heat the fuel in the unpurged fuel supply system, thereby causing the fuel to increase in pressure and incur the possibility of inadvertent opening of the fuel injector valve, thereby spraying fuel onto the hot combustion chamber walls. Such may result in the ignition of the fuel sprayed into the combustion chamber and generate flames through the turbine and into the engine exhaust duct. Since the engine is stopped and the aircraft is on the ground, such inadvertent ignition of fuel is a potential danger to ground personnel. This phenomenon is more common in hot weather and with highly volatile jet fuels, such as JP4.